The present invention relates to the art of earth boring, and more particularly, to an earth boring machine that produces a tunnel through the earth wherein portions of the earth formations at the face of the tunnel are broken away, falling to the tunnel invert. This type of earth boring machine is generally characterized by a rotary head connected to the body of the machine. The rotary head includes cutters for contacting the face of the bore and loosening material at the face. The cutters positioned on the periphery of the rotary head are referred to as gage cutters because they perform the function of maintaining full gage size of the tunnel. The material loosened by the cutters falls to the invert of the tunnel where it accumulates and must be picked up for removal. The removal is generally performed by buckets attached to the rotary head.
Gage cutter scrapers may be positioned immediately ahead of the gage cutters. The gage cutter scrapers clear a path through the material accumulated in the tunnel invert to protect the gage cutter from recutting or regrinding this material. The gage cutters are thus prevented from unnecessary wear. Since the gage cutter scrapers are subjected to severe abrasive wear, they must frequently be adjusted to maintain the desired clearance between them and the tunnel wall. One approach has been to utilize gravity-actuated scrapers which utilize the force of gravity acting on the scraper blades. The scraper blades are free to move in and out relative to the wall of the tunnel. There is a tendency for the clearance spaces on the gravity-actuated scraper blades to become impacted with muck and thus prevented from moving freely. Another approach is self-adjusting scraper blade assemblies. The self-adjusting scraper blade assemblies have springs that force the scraper blades outward maintaining contact with the tunnel wall. This type of scraper blade system has a tendency toward excessive scraper blade wear and for impacted debris to render the springs ineffective. Another approach is a manually adjusted scraper blade system. The manually adjusted scraper blades have a tendency to be difficult to adjust. Since the adjustment locking mechanisms must be sufficient to resist the forces tending to drive the scraper blades away from the tunnel wall, the locking mechanisms produce problems when it becomes time to adjust position of the scraper blades. For example, flat plate-type scraper blades secured by friction-type bolting arrangements must be clamped with a force of sufficient magnitude to prevent the force acting to drive the scraper blades away from the tunnel wall from displacing the scraper blades. The direct-acting friction joint must be of such size and requires such a number of bolts that problems arise in subsequently adjusting the position of the blades. It will therefore be appreciated that a need clearly exists for a gage cutter scraper that may be easily and quickly adjusted.